1. Field of the Invention
This invention is in the field of piezoelectric devices and more particularly it relates to a piezoelectric motor employing unique piezoelectric stacks and associated rotating components to provide a rotary actuator.
2. Description of the Prior Art
Pieoelectric actuators are known for their high output force, wide bandwidth response and high efficiency. Piezoelectric stacks have been constructed that operate in the extension mode, that is they become longer when a voltage is applied thereto. Piezoelectric stacks can also be made to operate in a shear mode if properly electrically poled so that the stack moves laterally rather than becoming longer. So far as known shear mode stacks made heretofore were capable only of motion along one axis. Controlled motion from piezoelectric actuators, including rotary motion, has been achieved but known actuators have been capable of only very small movement and limited power and speed. Prior devices have not fully capitalized on actuator potential. Miniature piezoelectric actuators developed by Micro Pulse Systems Inc. that are capable of linear and rotary motion are briefly described in an article entitled Piezoelectric Actuators Generate Many Motion Patterns appearing on page 136 of the 6-8-87 issue of Design News. A mount for a laser mirror that employs a piezoelectric actuator capable of shear type deformation along a single axis is disclosed in U.S. Pat. No. 4,775,815 issued to Theodore Heinz on Oct. 4, 1988. In the Heinz patent the shear motion of piezoelectric actuators are amplified by mechanical linkages connected between the piezoelectric actuators and the mirror mount.
Yet another known method of producing rotary motion from piezoelectric elements is the ultrasonic wave motor described on page 42 of the January 1988 issue of the Journal of Electric Engineering. In such a wave motor a traveling wave of acoustic energy is generated in a ring shaped elastic body by a ring shaped piezoelectric element adhered to the plastic body. The plastic body and piezoelectric element forms the stator of the motor. The traveling wave generates ripples or waves on the otherwise smooth surface of the stator that contact the surface of a rotor element mounted adjacent thereto and impart motion to the rotor. The wave motor can be made into a linear actuator by forming the stator and rotor in a line rather than ring shaped.